. A manual of zoology. Zoology. 88 GENEliAL Pl'JNCJI'LES OF ZOOLOGY. Formation of Bone.—I'he stratification of ?jone is caused by its mode of origin. Whore the bone borders upon the Haversian canals, the marro\y-cavity, and the periosteum, there is transiently or piermanently an epithelial-like layer of cells, odeohlads, which secrete the bone-substance on their surface. Certain cells in the matrix participate in this secretion, and here give rise to the bone-corpuscles, whicli are distinguished from the cartilage-cells by their numerous processes ramifying through the matrix. The processes of
. A manual of zoology. Zoology. 88 GENEliAL Pl'JNCJI'LES OF ZOOLOGY. Formation of Bone.—I'he stratification of ?jone is caused by its mode of origin. Whore the bone borders upon the Haversian canals, the marro\y-cavity, and the periosteum, there is transiently or piermanently an epithelial-like layer of cells, odeohlads, which secrete the bone-substance on their surface. Certain cells in the matrix participate in this secretion, and here give rise to the bone-corpuscles, whicli are distinguished from the cartilage-cells by their numerous processes ramifying through the matrix. The processes of a bone-corpuscle branch, and unite with the neighbor- ing cells through fusion of the processes, an arrangement most beautifully seen in dried bone, Ijecause here the cavities and the canals of the matrix are filled with air. Special modification of bony tissue, the substance of fish-scales and of the teeth, called also ivory or dentine, should be mentioned. Blood and Lymph, here treated in connexion with the connec- tive substances, are in reality not tissues at all, but nutritive fluids. Two kinds of nutritive fluids occur in the vertebrates, red blood and the colorless, weakly opalescent, or cloudy white lymijh. The Ijlood of man and other vertebrates, consists of a fluid and the organized constituents. The fluid or hlood-plasma is, aj^art from inorganic constituents, sjiecially rich in 23roteids; after tlie removal of the blood from the blood-vessels a jjart of these sej^arate by coagulation and form the blood-clot, made up of fibrin, leaving a fluid i^oor in proteids, the blood-serum. The organized con- ^ stituents, the hlood-ccUs, are disiin- guished as red and white blood-cor- puscles. The latter, the Icucoci/tes, are present in smaller numbers and have great similarity to the amtebaj found in water: they are particles of protoplasm, contain a nucleus, devour foreign lioilies (for example, I'arniine granules injected into the blood), and move in the ' anueboid "
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